One form of a conveyor ball unit for installation in a mounting opening in a conveyor track panel comprises a conveyor ball which is rotatably mounted on a plurality of mounting balls in a mounting shell and which projects upwardly out of the conveyor ball unit, with a ball guide or retainer embracing the conveyor ball from above in an annular configuration to secure the conveyor ball and the mounting balls in the mounting shell. At its peripheral edge the ball guide is provided with at least two locking elements each of which has a locking shoulder which in the assembled condition of the unit securingly engages under a peripheral flange on the mounting shell, thereby to hold the shell and ball guide together.
Conveyor ball units of that kind are used for example in ball-type conveyor tracks which are provided for example in the freight compartment of a freight aircraft, for moving freight containers when loading or unloading the aircraft. Under those conditions of use the conveyor ball units are subject in particular to the requirements that they should be maintenance-free and very robust, while nonetheless being low in weight.
In a particular configuration of a conveyor ball unit as generally discussed above, to be found in U.S. Pat. No. 4,871,052, the conveyor ball which is rotatably mounted on a plurality of mounting balls is combined together with a substantially hemispherical mounting shell and a ball guide which is connected thereto and which holds the conveyor ball on the mounting balls, to provide a mounting assembly. The mounting assembly is disposed in a substantially hollow-cylindrical housing movably along the centre line of the housing. The housing itself is then releasably fixed to the panel of a conveyor track. Arranged between the underside of the mounting shell and ribs in the lower portion of the housing is an array of plate springs for biasing the mounting unit, in the unloaded condition of the conveyor ball, upwardly in the housing until meeting an abutment shoulder, so that the conveyor ball projects upwardly through a central opening in the ball guide and beyond the surface of the panel of the conveyor track. When subjected to a loading by a freight container, the conveyor ball together with the entire mounting assembly can be urged resiliently downwardly into the housing against the force of the plate springs, until the spring travel of the array of plate springs has been totally utilised.
Although, generally speaking, the resilient configuration of the conveyor ball unit is highly desirable because of the severe requiremens occuring in a freight loading situation, nonetheless in practice there are some situations of use in which it is impossible to forego the resilient action of the unit and instead the predominant consideration is that the conveyor ball unit should be of a minimum weight.